System and method for multiple level facet joint arthroplasty and fusion

ABSTRACT

Facet joint replacement implants may be designed for use on multiple adjacent vertebral levels. Each superior implant may have a substantially semispherical concave surface, and each inferior implant may have a cooperating semispherical convex surface that is deformable to enable it to be pressed into the superior implant concave surface to fix the relative orientations of the superior and inferior implants. Thus, the inferior implant may be attached to the same pedicle as the superior implant, but may also be oriented independently of the superior implant and then fixed in position. Similar mounting structures may be used to attach one or more fusion implants to a level adjacent to that of a facet joint replacement implant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 12/240,512, filedSep. 29, 2008, which is a divisional of the following:

U.S. application Ser. No. 11/463,513, filed Aug. 9, 2006, now issued asU.S. Pat. No. 8,562,649, and is entitled SYSTEM AND METHOD FOR MULTIPLELEVEL FACET JOINT ARTHROPLASTY AND FUSION, which claims the benefit ofthe following U.S. Application No. 60/760,863, filed Jan. 19, 2006, andis entitled MULTI-LEVEL FACET ARTHROPLASTY WITH ADJACENT LEVEL FUSION.All of these references are incorporated herein by reference in theirentireties.

The following documents are also incorporated herein by reference intheir entireties:

U.S. application Ser. No. 10/687,856, filed Oct. 17, 2003, and isentitled FACET JOINT REPLACEMENT;

U.S. application Ser. No. 10/860,778, filed Jun. 2, 2004, and isentitled SPINAL FACET IMPLANT WITH SPHERICAL IMPLANT APPOSITION SURFACEAND BONE BED AND METHODS OF USE;

U.S. application Ser. No. 10/860,543, filed Jun. 2, 2004, and isentitled SPINAL FACET IMPLANTS WITH MATING ARTICULATING BEARING SURFACEAND METHODS OF USE;

U.S. application Ser. No. 10/860,495, filed Jun. 2, 2004, and isentitled LINKED BILATERAL SPINAL FACET SUPERIOR AND INFERIOR IMPLANTSAND METHODS OF USE;

U.S. application Ser. No. 10/860,487, filed Jun. 2, 2004, and isentitled SPINAL FACET JOINT IMPLANT;

U.S. application Ser. No. 10/990,191, filed Nov. 15, 2004, and isentitled SURGICAL MEASUREMENT AND RESECTION FRAMEWORK;

U.S. application Ser. No. 10/989,971, filed Nov. 15, 2004, and isentitled SURGICAL MEASUREMENT SYSTEMS AND METHODS;

U.S. application Ser. No. 11/063,941, filed Feb. 22, 2005, and isentitled POLYAXIAL ORTHOPEDIC FASTENING APPARATUS;

U.S. application Ser. No. 11/388,389, filed Mar. 24, 2006, and isentitled POLYAXIAL REAMING APPARATUS AND METHOD;

U.S. application Ser. No. 11/312,323, filed Feb. 22, 2005, and isentitled POLYAXIAL ORTHOPEDIC FASTENING APPARATUS WITH INDEPENDENTLOCKING MODES;

U.S. Application No. 60/757,592, filed Jan. 9, 2006, and is entitled AFRSURGICAL INSTRUMENTATION AND TECHNIQUE; and

U.S. application Ser. No. 11/350,179, filed Feb. 7, 2006, and isentitled FACET JOINT IMPLANT CROSSLINKING APPARATUS AND METHOD.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to orthopedic implants andassociated methods, and more particularly, to facet joint replacementimplants and methods.

2. The Relevant Technology

Many people experience back pain. Back pain is not only uncomfortable,but can be particularly debilitating. Many people who wish toparticipate in sports, manual labor, or even sedentary employment areunable to do so because of pains that arise from motion of or pressureon the spinal column. Such pains are often caused by traumatic,inflammatory, metabolic, synovial, neoplastic and degenerative disordersof the spine.

In order to alleviate such injuries and pains, spinal fusion techniqueshave been used for many years to essentially lock two vertebraetogether. More recently, artificial discs have been used to replacenatural intervertebral discs to correct disc pathologies, while stillpermitting the adjacent vertebrae to move with respect to each other.Various implants have also been proposed for the partial or completereplacement of vertebral facet joints to alleviate discomfort associatedwith diseased or atrophied articular processes, while still permittingintervertebral motion.

One deficiency in many of the proposed implants and methods is that theyonly permit the replacement of articular surfaces on a single vertebrallevel (i.e., a single “facet joint”). Many known devices are attached toa vertebra in such a manner that a similar device for an adjacent levelcannot be attached to the same vertebra. Accordingly, facet jointpathologies that extend along multiple joints cannot effectively becorrected.

Another deficiency in many of the proposed implants and methods is that,once an implant has been used to replace part or all of a single facetjoint, the implant interferes with the use of another implant to fuse anadjacent vertebral level. Accordingly, the correction of spinalpathologies extending along multiple vertebral joints is furtherinhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1 is a perspective view of a system according to one embodiment ofthe invention, in which multiple level facet joint replacement may becarried out with adjacent level fusion.

FIG. 2 is an exploded, perspective view of the caudal facet jointassembly, fixation members, and locking assemblies of the system of FIG.1.

FIG. 3 is an exploded, perspective view of the caudal fusion assembly,fixation members, and yoke assemblies of the system of FIG. 1.

FIG. 4 is an exploded, perspective view of the cephalad fusion assembly,fixation members, and yoke assemblies of the system of FIG. 1.

FIG. 5 is a perspective view of a system according to one alternativeembodiment of the invention, in which multiple level facet jointreplacement may be carried out without adjacent level fusion.

FIG. 6 is a perspective view of one of the engagement members of thesystem of FIG. 5.

FIG. 7 is a perspective view of one of the in-growth cups of the systemof FIG. 5.

FIG. 8 is a perspective view of a portion of a spine to which the systemof FIG. 1 or the system of FIG. 5 may be secured to provide multiplelevel facet joint replacement with or without adjacent level fusion.

FIG. 9 is a perspective view of the portion of the spine of FIG. 8 afterresection of some of the natural articular surfaces of the vertebrae.

FIG. 10 is a perspective view of the portion of the spine of FIG. 8after implantation of guide wires in the pedicles of some of thevertebrae.

FIG. 11 is a perspective view of the portion of the spine of FIG. 8after reaming of the pedicle saddle points to provide semisphericalresections.

FIG. 12 is a perspective view of the portion of the spine of FIG. 8 witha frame registered on the third vertebra to facilitate formation ofshaped resections on the saddle points of the second vertebra.

FIG. 13 is a perspective view of the portion of the spine of FIG. 8after attachment of the caudal fusion assembly and the superiorprostheses of the caudal facet joint assembly of the system of FIG. 1 tothe portion of the spine.

FIG. 14 is a perspective view of the portion of the spine of FIG. 8 withthe frame registered on the fourth vertebra to facilitate formation ofshaped resections on the saddle points of the third vertebra.

FIG. 15 is a perspective view of the portion of the spine of FIG. 8after further attachment of the inferior prostheses of the caudal facetjoint assembly and the superior prostheses of the cephalad facet jointassembly of the system of FIG. 1 to the portion of the spine.

FIG. 16 is a perspective view of the portion of the spine of FIG. 8 withthe frame registered on the fifth vertebra to facilitate formation ofshaped resections on the saddle points of the fourth vertebra.

FIG. 17 is a perspective view of the portion of the spine of FIG. 8after further attachment of the inferior prostheses of the cephaladfacet joint assembly of FIG. 1 and a cephalad fusion assembly to theportion of the spine.

FIG. 18 is a perspective view of the portion of the spine of FIG. 8 withthe system of FIG. 5 attached thereto instead of the system of FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to facet joint replacement implants thatcan be applied to multiple adjacent vertebral levels and/or used withadjacent-level fusion implants. The facet joint replacement implants andfusion implants are independently orientable at each vertebral level tocompensate for natural variations in spinal morphology.

Referring to FIG. 1, a perspective view illustrates a system 10according to one embodiment of the invention, in which multiple levelfacet joint replacement may be carried out with adjacent level fusion.The directional arrows of FIG. 1 illustrate how the system 10 would beoriented with respect to a human spine by illustrating a cephaladdirection 12, a caudal direction 14, an anterior direction 16, aposterior direction 18, and a medial/lateral direction 20.

The configuration of the system 10 will be explained in the descriptionsof FIGS. 1 through 4, and the configuration of an alternative systemwithout adjacent level fusion will be explained in the descriptions ofFIGS. 5 through 7. One method of implanting the system 10 and securingit to a portion of a human spine will be shown and described inconnection with FIGS. 8 through 16, and implantation of the alternativesystem will be set forth in the description of FIG. 18.

In the embodiment of FIG. 1, the system 10 includes a caudal facet jointassembly 24, a cephalad facet joint assembly 26, a caudal fusionassembly 28, and a cephalad fusion assembly 30. Each of the facet jointassemblies 24, 26 provides replacement (i.e., arthroplasty) of the facetarticular surfaces of one “facet joint,” which includes the two superiorarticular surfaces of one vertebra and the two inferior articularsurfaces of a second vertebra superior to the first vertebra. The facetjoint assemblies 24, 26 may substantially duplicate the shapes andorientations of the natural articular surfaces so that they providenatural, or “anatomic” articulation that feels to the patient like thenatural motion of a healthy spinal joint.

The caudal fusion assembly 28 is designed to substantially immobilizeone facet joint by substantially preventing relative motion between twovertebrae. The cephalad fusion assembly 30 is designed to substantiallyimmobilize two facet joints by substantially preventing relative motionbetween three vertebrae. If desired, the caudal fusion assembly 28and/or the cephalad fusion assembly 30 may be used on combination withother implants such as intervertebral spacers, fusion cages, anteriorplates to enhance the stability and/or fusion of the joints involved.The use of such implants is known in the art; accordingly, they are notdescribed herein.

If desired, the system 10 may be applied to the sacrum and the lumbarvertebrae, such that the caudal fusion assembly 28 immobilizes the jointbetween S1 and L5, the caudal facet joint assembly 24 provides motion ofthe joint between L5 and L4, the cephalad facet joint assembly 26provides motion of the joint between L4 and L3, and the cephalad fusionassembly immobilizes the joint between L3 and L2 and the joint betweenL2 and L1. However, the present invention is not limited tolumbar/sacral applications, and the implants and techniques illustratedmay be readily adapted by one of skill in the art for use with thoracicvertebrae, cervical vertebrae, and/or any combination of spinalvertebrae and the sacrum.

As shown, the caudal facet joint assembly 24 has a left superiorprosthesis 34, a right superior prosthesis 36, a left inferiorprosthesis 38, and a right inferior prosthesis 40. The superiorprostheses 34, 36 are shaped to replace the superior articular surfacesof a vertebra, and the inferior prostheses 38, 40 are shaped to replacethe inferior articular surfaces of an adjacent vertebra. Due to naturalvariations in vertebral articular processes, the superior prostheses 34,36 need not be mirror images of each other, and the inferior prostheses38, 40 also need not be mirror images of each other. Rather, each of theprostheses 34, 36, 38, 40 of the caudal facet joint assembly 24 may beselected from a kit of differently-dimensioned prostheses designed foruse with a wide variety of vertebral morphologies.

Furthermore, the left and right inferior prostheses 38, 40 may besecured together through the use of a crosslink assembly 42. Thecrosslink assembly 42 substantially prevents relative motion between theleft and right inferior prostheses 38, 40 to ensure that they do notshift under the loads produced by articulation with the superiorprostheses 34, 36. The crosslink assembly 42 may be designed to beattachable in loose form to the inferior prostheses 38, 40 so that theprostheses 38, 40 can be reoriented prior to tightening of the crosslinkassembly 42 to a rigid state.

As also shown, the cephalad facet joint assembly 26 has a left superiorprosthesis 44, a right superior prosthesis 46, a left inferiorprosthesis 48, and a right inferior prosthesis 50. The inferiorprostheses 48, 50 may be secured together through the use of a crosslink52. The prostheses 44, 46, 48, 50 and the crosslink 52 of the cephaladfacet joint assembly 26 may be configured similarly to the prostheses34, 36, 38, 40 and the crosslink 42 of the caudal facet joint assembly24. However, due to variations in bone structures between adjacentvertebrae, the prostheses 44, 46, 48, 50 and the crosslink 52 need notbe identical to the prostheses 34, 36, 38, 40 and the crosslink 42.

The prostheses 34, 36, 38, 40, 44, 46, 48, 50 of the caudal facet jointassembly 24 and the cephalad facet joint assembly 26 may be secured tovertebrae through the use of fixation members, in the form of pediclescrews 54, and locking assemblies 56. The locking assemblies 56 may beused to independently lock out rotational and translational motion ofthe prostheses 34, 36, 38, 40, 44, 46, 48, 50 relative to the pediclescrews 54. The inferior prostheses 38, 40 of the caudal facet jointassembly 24 may be shaped to nest within the superior prostheses 44, 46of the cephalad facet joint assembly 26 so that the inferior prostheses38, 40 and the superior prostheses 44, 46 can be secured to thecorresponding vertebra through the use of a single pair of pediclescrews 54 and locking assemblies 56.

The caudal fusion assembly 28 may have a left superior prosthesis 60, aright superior prosthesis 62, and two rods 64. The superior ends of therods 64 may be secured to the corresponding vertebra via the superiorprostheses 60, 62. The inferior ends of the rods 64 may be secured tothe immediately inferior vertebra through the use of pedicle screws 66and yoke assemblies 68. The superior prostheses 60, 62 are shaped tonest within the superior prostheses 34, 36 of the caudal facet jointassembly such that the superior prostheses 60, 62 and the superiorprostheses 34, 36 can be secured to the corresponding vertebra with asingle pair of pedicle screws 54 and locking assemblies 56.

The cephalad fusion assembly 30 may have a left inferior prosthesis 72,a right inferior prosthesis 74, a pair of rods 76, a pair of polyaxialrod connectors 78, and a crosslink assembly 82. The inferior ends of therods 76 may be secured to the corresponding vertebra via the inferiorprostheses 72, 74. The central portions of the rods 76 and the superiorends of the rods 76 may be secured to the two immediately superiorvertebrae through the use of pedicle screws 66 and yoke assemblies 68like those used in connection with the caudal fusion assembly 28. Thecrosslink assembly rigidly connects the rods 76 together to maintain therigidity of the cephalad fusion assembly 30. The inferior prostheses 48,50 of the cephalad facet joint assembly 26 are shaped to nest within theinferior prostheses 72, 74 of the cephalad fusion assembly 30 such thatthe inferior prostheses 48, 50 and the inferior prostheses 72, 74 can besecured to the corresponding vertebra with a single pair of pediclescrews 54 and locking assemblies 56.

It will be appreciated by those of skill in the art that the variousassemblies 24, 26, 28, 30 can be interchanged in modular fashion andapplied in a variety of combinations to treat spinal disorders occurringacross multiple joint motion segments. Thus, the specific needs of thepatient can be accurately addressed. Fusion and facet joint replacementcan be applied to adjacent or non-adjacent vertebral levels, or eitherfusion or facet joint replacement can be exclusively utilized.

Referring to FIG. 2, an exploded, perspective view illustrates thecaudal facet joint assembly 24, pedicle screws 54, and lockingassemblies 56 of the system 10 of FIG. 1. As shown, each of the superiorprostheses 34, 36 has a bone apposition surface 90, a semisphericalreceiving surface 92, and an articulation surface 94. Each boneapposition surface 90 is part of a mounting portion of the correspondingprosthesis 34 or 36, and may be generally conical in shape, withprotruding fingers designed to engage the vertebral bone to preventrelative motion between the superior prostheses 34, 36 and the vertebrato which they are attached.

Each semispherical receiving surface 92 has a substantially concave,semispherical shape sized to receive the corresponding convex,semispherical portion of any of the superior prostheses 60, 62, theinferior prostheses 38, 40, or the inferior prostheses 48, 50. Eacharticulation surface 94 has a shape that is shaped to articulate withthe corresponding inferior prosthesis 38 or 40. The articulationsurfaces 94 may mimic the shapes of the natural superior facets, and maythus have concave, trough-like shapes or the like.

Each of the inferior prostheses 38, 40 may have a semisphericalengagement surface 100, a semispherical receiving surface 102, anarticulation surface 104, and a stem 106. The semispherical engagementsurfaces 100 have substantially convex, semispherical shapes sized tonest within the semispherical receiving surfaces 92 of the superiorprostheses 34, 36. The semispherical shapes of the semisphericalreceiving surfaces 92 and semispherical engagement surfaces 100 permitpolyaxial adjustment of the orientation of each inferior prosthesis 38,40 relative to the corresponding superior prosthesis 34, 36.

In this application, “polyaxial adjustability” refers to the ability torotate the object about at least two, and possibly three, orthogonalaxes relative to another object. Through the use of polyaxialadjustability, the facet joint assemblies 24, 26 are adjustable toaccommodate a wide variety of spinal morphologies, and providerelatively natural articulation regardless of natural variations invertebral geometry.

The semispherical engagement surfaces 100 may optionally be broken byslots, as shown in FIG. 2. The slots in the semispherical engagementsurfaces 100 permit the semispherical engagement surfaces to contract asthey are urged into the semispherical receiving surfaces 92. Theresulting expansion pressure holds the semispherical engagement andreceiving surfaces 100, 92 tightly together to restrict relative motionbetween the superior prostheses 34, 36 and the inferior prostheses 38,40 after the locking assemblies 56 have been tightened on the pediclescrews 54.

The semispherical receiving surfaces 102 of the inferior prostheses 38,40 have substantially concave, semispherical shapes that aresubstantially concentric with the semispherical engagement surfaces 100.The semispherical receiving surfaces 102 are sized to receivecorresponding convex, semispherical surfaces of the locking assemblies56, as will be described in detail subsequently.

The articulation surfaces 104 are shaped to articulate with thearticulation surfaces 94 of the superior prostheses 34, 36 in a mannerthat substantially duplicates the articulation of the natural facetjoint replaced by the superior and inferior prostheses 34, 36, 38, 40.Thus, the articulation surfaces 104 may mimic the shapes of the naturalinferior facets, and may have convex shapes. Each stem 106 connects oneof the semispherical engagement surfaces 100 with the correspondingarticulation surface 104 such that, upon attachment of the inferiorprostheses 38, 40 to the pedicles of the corresponding vertebra, thearticulation surfaces 104 are positioned at or near the locations of theremoved natural inferior facets.

As also shown in FIG. 2, the crosslink assembly 42 includes two implantcoupling components 110, two bolts 112, two rod coupling components 114,two nuts 116, and a rod 118. The implant coupling components 110 areshaped to be attached to the inferior prostheses 38, 40 in a manner thatpermits adjustment of the positioning of the implant coupling components110 relative to the inferior prostheses 38, 40 along an axis extendinggenerally anterior-posteriorly.

The bolts 112 can pass through holes in the implant coupling components110 and through aligned holes in the rod coupling components 114 so thatthe rod coupling components 114 can be pivotably adjusted about the axesof the bolts 112 and locked in place relative to the implant couplingcomponents 110 through the use of the nuts 116. The bolts 112 and nuts116 are also used to secure the rod coupling components 114 to the endsof the rod 118 at the desired spacing. Thus, the crosslink assembly 42is adjustable to suit the spacing and angulation of the inferiorprostheses 38, 40, and is also easily lockable through the use of thebolts 112 and nuts 116 to provide a rigid bridge between the inferiorprostheses 38, 40.

As also illustrated in FIG. 2, each of the pedicle screws 54 has aproximal end 130 that receives the corresponding locking assembly 56,and a distal end 132 with threads that facilitate implantation of thedistal end 132 in the bone of the corresponding vertebra. Each proximalend 130 has a sliding interface with a substantially continuous crosssection, along which the corresponding locking assembly 56 canselectively slide. In FIG. 2, the sliding interfaces are polygonalportions 134 having octagonal cross sectional shapes. Other crosssectional shapes may, of course, be used to provide a sliding interface.Each proximal end 130 also has threads 136 designed to receive thecorresponding locking assembly 56, and a torquing interface 138 that canbe engaged by a tool to facilitate implantation of the pedicle screw 54in the corresponding vertebra.

Each of the locking assemblies 56 includes an interpositional member140, an engagement member 142, a rotational locking member 144, and atranslational locking member 146. Each interpositional member 140 hasexterior threads, a flared end, and a bore shaped to slide along thepolygonal portion 134 of the corresponding pedicle screw 54. Eachengagement member 142 may take the form of a split sphere 142 with aplurality of slots that permit expansion and contraction of the splitsphere 142. Each split sphere 142 has a hollow interior in which thecorresponding interpositional member 140 may be positioned, such thatthe flared end of the interpositional member protrudes from the distalend of the split sphere 142.

Each of the rotational locking members 144 includes interior threadsthat engage the exterior threads of the corresponding interpositionalmember 140. Thus, the split sphere 142 may be compressed between therotational locking member 144 and the flared end of the attachedinterpositional member 140. In response to the compression, the flaredend urges outward expansion of the split sphere 142 so that the outersurface of the split sphere 142 engages the semispherical receivingsurface 102 of the corresponding inferior prosthesis 38 or 40. Due tothe slotted geometry of the semispherical engagement surface 100, theresulting radial pressure on the semispherical receiving surface 102causes expansion of the corresponding semispherical engagement surface100. Thus, the semispherical engagement surface 100 expands to pressagainst the semispherical receiving surface 92 of the correspondingsuperior prosthesis 34 or 36.

Accordingly, threaded tightening of a rotational locking member 144relative to an interpositional member 140, with the interpositionalmember 140 positioned on the polygonal portion 134 of a pedicle screw54, restricts relative rotation between the pedicle screw 54, thelocking assembly 56, the inferior prosthesis 38 or 40, and the superiorprosthesis 34 or 36. Advantageously, the locking assembly 56 is stillslidable along the pedicle screw 54 until the associated translationallocking member 146 is tightened on the threads 136 of the proximal end130 of the pedicle screw 54. Once the translational locking member 146is tightened, it presses the remainder of the locking assembly 56, theinferior prosthesis 38 or 40, and the superior prosthesis 34 or 36against the bony apposition surface of the corresponding vertebra toprevent further sliding of the locking assembly 56, the inferiorprosthesis 38 or 40, and the superior prosthesis 34, 36 relative to thepedicle screw 54.

Referring to FIG. 3, an exploded, perspective view illustrates thecaudal fusion assembly 28, pedicle screws 66, and yoke assemblies 68 ofthe system 10 of FIG. 1. As shown, each of the inferior prostheses 60,62 has a semispherical engagement surface 150, a semispherical receivingsurface 152, a yoke assembly 154, and a stem 156. Each semisphericalengagement surface 150 has a convex, substantially semispherical shapesized to nest within the semispherical receiving surface 92 of thecorresponding superior prosthesis 34 or 36. Each semisphericalengagement surface 150 may optionally have a slotted configuration likethat of the semispherical engagement surfaces 100 of the inferiorprostheses 38, 40 shown in FIG. 2. However, as embodied in FIG. 3, thesemispherical engagement surfaces 150 are not slotted.

Each of the semispherical receiving surfaces 152 has a concave,substantially semispherical shape sized to receive the outer surfaces ofthe split spheres 142 of the locking assemblies 56 in a manner similarto that of the semispherical receiving surfaces 102 of the inferiorprostheses 38, 40. Each yoke assembly 154 is shaped to receive thecephalad end of one of the rods 64. The yoke assemblies 154 areconnected to the semispherical engagement surfaces 150 by the stems 156.

The pedicle screws 66 are configured differently from the pedicle screws54 because the pedicle screws 66 are designed to receive the yokeassemblies 68 instead of the locking assemblies 56. Thus, each of thepedicle screws 66 has a proximal end 158 and a distal end 160. Theproximal end 158 may have a head (not visible) with a semisphericalundercut that permits polyaxial rotation of the corresponding yokeassembly 68 relative to it, until the yoke assembly 68 is locked. Eachdistal end 160 may be threaded to permit implantation in the pedicle ofa vertebra.

Each of the yoke assemblies 68, 154 may have a configuration similar tothat of known polyaxial yokes, or may be configured differently fromknown systems. As embodied in FIG. 3, each yoke assembly 68, 154 has afirst wall 162 and a second wall 164 that extend generally parallel toeach other to define a trough 166 that extends between the first andsecond walls 162, 164. Each of the first and second walls 162, 164 hasthreads (not shown) on the interior, concave surface. Each yoke assembly68, 154 may also have a nut 168 with exterior threads (not shown) thatcan be threadably engaged with the threads of the corresponding walls162, 164 to advance the nut 168 toward the trough 166.

When the ends of the rods 64 are positioned in the troughs 166 of theyoke assemblies 68, 154, tightening the nuts 168 causes the nuts 168 topress the ends of the rods 64 into the troughs 166 such that the ends ofthe rods 64 are captured by the yoke assemblies 68, 154. In the case ofthe yoke assemblies 68, tightening the nuts 168 against the ends of therods 64 may also cause the rods 64 to press against the proximal ends ofthe pedicle screws 66, thereby restricting or preventing relativerotation between the yoke assemblies 68 and the pedicle screws 66.Advantageously, the polyaxial adjustability of the yoke assemblies 68prior to tightening of the nuts 168 permits attachment of the caudalends of the rods 64 to the pedicle screws 66 at a wide variety ofrelative orientations, thereby permitting the caudal fusion assemblywith a wide variety of spinal morphologies.

Referring to FIG. 4, an exploded, perspective view illustrates thecephalad fusion assembly 30, pedicle screws 66, and yoke assemblies 68of the system of FIG. 1. As shown, each of the inferior prostheses 72,74 of the cephalad fusion assembly 30 has a bone apposition surface 180,a semispherical receiving surface 182, a polyaxial receiver 184, and areceiver fastener 186.

The bone apposition surfaces 180 are substantially the same as the boneapposition surfaces 90 of the superior prostheses 34, 36 of the caudalfacet joint assembly 24. Thus, each of the bone apposition surfaces 180may be generally conical in shape, with protruding fingers designed toengage the vertebral bone to prevent relative motion between theinferior prostheses 72, 74 and the vertebra to which they are attached.

The semispherical receiving surfaces 182 may be substantially the sameas the semispherical receiving surfaces 92 of the superior prostheses34, 36 of the caudal facet joint assembly. Thus, each of thesemispherical receiving surfaces 182 may have a substantially concave,semispherical shape sized to receive the corresponding convex,semispherical portion of any of the superior prostheses 60, 62, theinferior prostheses 38, 40, or the inferior prostheses 48, 50.

Each of the rod connectors 78 may have a substantially semisphericalshape with slots that permit expansion or contraction of the rodconnectors 78. The rod connectors 78 may have bores (not visible) sizedto receive the caudal ends of the rods 76. The exterior surfaces of therod connectors 78 may be compressed to substantially radially compressthe caudal ends of the rods 76, thereby providing a tight attachmentbetween the rod connectors 78 and the caudal ends of the rods 76.

Each of the polyaxial receivers 184 extends form the corresponding boneapposition surface 180 and has a concave, semispherical bore (notvisible) shaped to receive the corresponding polyaxial rod connector 78in a manner that permits polyaxial rotation between the rod connector 78and the polyaxial receiver 184. Thus, each polyaxial receiver 184 canreceive the caudal end of the corresponding rod 76 at any of a pluralityof relative orientations. This permits usage of the cephalad fusionassembly 30 with a wide variety of spinal morphologies.

The receiver fasteners 186 are used to tighten the concave,semispherical bores of the polyaxial receivers 184 around the rodconnectors 78. The receiver fasteners 186 may take the form of smallscrews that can be tightened to cause contraction of the concave,semispherical bores of the polyaxial receivers 184 around the rodconnectors 78. In response to contraction of the concave, semisphericalbores, the rod connectors 78 tighten around the caudal ends of the rods76 so that the rods 76 become rigidly secured to the inferior prostheses72, 74.

The pedicle screws 66 and yoke assemblies 68 are identical to thosedescribed in connection with FIG. 3. Accordingly, the yoke assemblies 68are polyaxially rotatable relative to the pedicle screws 66 to permitthem to receive the cephalad ends of the rods 76 at any of a pluralityof relative orientations. Like those of FIG. 3, the orientations of theyoke assemblies 68 may also be locked relative to the pedicle screws 66by tightening the nuts 168 against the cephalad ends of the rods 76.

As embodied in FIG. 4, the crosslink assembly 82 is very similar to thecrosslink assemblies 42, 52 of the facet joint assemblies 24, 26.Accordingly, the crosslink assembly 82 has two rod coupling components190, two bolts 112, two rod coupling components 114, two nuts 116, and arod 118. The rod coupling components 190 may be very similar to theimplant coupling components 110 of the crosslink assemblies 42, 52,except that the rod coupling components 190 are sized to grip the rods76 of the caudal fusion assembly 28 instead of the inferior prostheses38, 40. The bolts 112, 114, nuts 116, and rod 118 function in a mannervery similar to that described in connection with FIG. 2, in thedescription of the crosslink assembly 42 of the caudal facet jointassembly 24. Thus, the crosslink 82 may be adjusted to accommodatedifferent positions of the rods 76, and may then be tightened to providea rigid bridge between the rods 76.

The system 10 of FIG. 1 effectively replaces the natural facets of twospinal motion segments with prosthetic facets, fuses the motion segmentimmediately inferior to the prosthetic facets, and also fuses the twomotion segments immediately superior to the prosthetic facets. Thesystem 10 is modular in design, and can therefore be used for anycombination of facet joint replacement and fusion, whether one ormultiple motion segments are to receive facet joint replacement orfusion, and whether or not the motion segments to be treated areadjacent to each other.

Referring to FIG. 5, a perspective view illustrates a system 210according to one alternative embodiment of the invention, in whichmultiple level facet joint replacement may be carried out withoutadjacent level fusion. As shown, the system 210 includes the caudalfacet joint assembly 24 and the cephalad facet joint assembly 26 ofFIG. 1. However, the caudal fusion assembly 28 and the cephalad fusionassembly 30 have been omitted.

In place of the caudal locking assemblies 56 of the caudal facet jointassembly 24, locking assemblies 240 are provided. Since the caudalfusion assembly 28 is not present, the superior prostheses 60, 62 of thecaudal fusion assembly 28 are not nested within the semisphericalreceiving surfaces 92 of the superior implants 34, 36 of the caudalfacet joint assembly 24. To fill the space that would otherwise be takenby the superior prostheses 60, 62, the locking assemblies 240 includeengagement members 242 that take the place of the split spheres 142included in the locking assemblies 56. The engagement members 242 arelarger than the split spheres 142 and will be shown and described inconnection with FIG. 6.

The inferior prostheses 72, 74 of the cephalad fusion assembly 30 alsoare not present. To fill the space that would otherwise be taken the byinferior prostheses 72, 74, in-growth cups 272 may be provided. Thein-growth cups receive the semispherical engagement surfaces 100 of theinferior prostheses 48, 50 of the cephalad fusion assembly 26 in amanner similar to that of the inferior prostheses 72, 74, as will bedescribed in connection with FIG. 7.

Advantageously, the remaining components of the system 210 aresubstantially the same as those of the system 10. Accordingly, a kit caneasily be provided, including the facet joint assemblies 24, 26, fusionassemblies 28, 30, pedicle screws 54, 66, locking assemblies 56, yokeassemblies 68, engagement members 242, and in-growth cups 272. Such akit would enable the surgeon to select the components needed for eitherof the systems 10, 210, thereby providing maximum flexibility andminimizing inventory.

Referring to FIG. 6, a perspective view illustrates one of theengagement members 242 of the system 210 of FIG. 5. As shown, theengagement member 242 has an interior surface 282 with a generallycylindrical shape broken by slots 284. The engagement member 242 alsohas a proximal shoulder 286 and a distal shoulder 288. Like those of thesplit spheres 142, the proximal shoulder 286 of the engagement member242 may receive pressure from the associated rotational locking member144 to urge the distal shoulder 288 to slide over the flared portion ofthe corresponding interpositional member 140, thereby causing expansionof the distal portion of the engagement member 242.

The outer surface of the engagement member 242 then presses directlyagainst the semispherical receiving surface 92 of the correspondingsuperior prosthesis 34 or 36 of the caudal facet joint assembly 24. Thelarger size of the engagement members 242 relative to the split spheres142 enables the locking assemblies 240 to operate in a manner similar tothat of the locking assemblies 56, without requiring the presence of thesuperior prostheses 60, 62 of the caudal fusion assembly 28.

Referring to FIG. 7 a perspective view illustrates one of the in-growthcups 272 of the system 210 of FIG. 5. As shown, the in-growth cup 272has a bone apposition surface 290 and a semispherical receiving surface292. The bone apposition surface 290 may be semispherical as illustratedin FIG. 7, or may be shaped differently. For example, in alternativeembodiments, an in-growth cup (not shown) may have a bone appositionsurface with a generally conical shape, with or without the fingersutilized by the bone apposition surfaces 90 of the superior prostheses34, 36, 44, 46. The bone apposition surface 290 may also be porousand/or textured to facilitate bone in-growth into the in-growth cup 272.

The semispherical receiving surface 292 may be shaped substantially thesame as the semispherical receiving surfaces 92 of the superiorprostheses 34, 36, 44, 46. Accordingly, the semispherical receivingsurface 292 may be sized to receive the corresponding convex,semispherical portion of any of the superior prostheses 60, 62, theinferior prostheses 38, 40, or the inferior prostheses 48, 50. Thus, thein-growth cups 272 fill the spaces left by the omission of the inferiorprostheses 72, 74 of the cephalad fusion assembly 30.

Facet joint replacement and/or fusion systems according to the inventionmay be implanted through the use of a wide variety of procedures. FIGS.8 through 17 illustrate one procedure by which a system similar to thesystem 10 of FIG. 1 may be implanted. The system to be shown in FIGS. 8through 17 provides facet joint replacement for two adjacent spinalmotion segments, and fusion for the motion segments immediately inferiorand superior to them.

Referring to FIG. 8, a perspective view illustrates a portion of a spine300 to which the system 10 of FIG. 1 or the system 210 of FIG. 5 may besecured to provide multiple level facet joint replacement with orwithout adjacent level fusion. As shown, the spine 300 includes a firstvertebra 302, a second vertebra 304, a third vertebra 306, a fourthvertebra 308, and a fifth vertebra 310. The vertebrae 302, 304, 306,308, 310 may represent S1, L5, L4, L3, and L2, respectively.Alternatively, the vertebrae 302, 304, 306, 308, 310 may represent othervertebrae of the spine 300.

As illustrated in FIG. 8, the vertebrae 302, 304, 306, 308, 310 havemany anatomical structures known to those of skill in the art. Theseanatomical structures include pedicles 314 of the second vertebra 304,pedicles 316 of the third vertebra 306, pedicles 318 of the fourthvertebra 308, and pedicles 320 of the fifth vertebra 310.

The articular processes of the vertebrae 304, 306, 308, 310 may first beresected. The articular processes providing the joints between thesecond and third vertebrae 304, 306 and between the third and fourthvertebrae 306, 308 are resected to enable their prosthetic counterpartsto be positioned in such a manner that substantially naturalarticulation is provided. The articular processes providing the jointsbetween the first and second vertebrae 302, 304 and between the fourthand fifth vertebrae 308, 310 may be left intact because they may notinterfere with implantation of the fusion components. Alternatively, thearticular processes providing the joints between the first and secondvertebrae 302, 304 and/or between the fourth and fifth vertebrae 308,310 may be resected to facilitate implantation of the fusion componentsand/or to remove diseased or brittle bone.

Referring to FIG. 9, a perspective view illustrates the portion of thespine 300 of FIG. 8 after resection of some of the natural articularsurfaces of the vertebrae 304, 306, 308, 310. More precisely, thesuperior and inferior articular processes of the second vertebra 304have been resected away, leaving two inferior resections 330 and twosuperior resections 332. The superior and inferior articular processesof the third vertebra 306 have been resected away, leaving two inferiorresections 334 and two superior resections 336. The superior andinferior articular processes of the fourth vertebra 308 have beenresected away, leaving two inferior resections 338 and two superiorresections 340. The inferior articular processes of the fifth vertebra310 have been resected away, leaving two inferior resections 342.

According to one exemplary method, the resections 330, 332, 334, 336,338, 340, 342 need not be made at any precise angle or location. Afterthe articular processes have been resected away, guide wires may beimplanted in the vertebrae 304, 306, 308, 310. The guide wires may beused to guide further steps.

Referring to FIG. 10, a perspective view illustrates the portion of thespine 300 of FIG. 8 after implantation of guide wires 350 in thepedicles 314, 316, 318, 320 of the second, third, fourth, and fifthvertebrae 304, 306, 308, 310. The guide wires 350 may be configured andimplanted in a variety of ways, many of which are known in the art. Eachguide wire 350 is implanted along the axis of one of the pedicles 314,316, 318, 320. If the first vertebra 302 is S1, guide wires 350 may notbe needed in the first vertebra 302 to locate sufficient bone mass foranchoring the caudal fusion assembly 28 to the first vertebra 302. Afterthe guide wires 350 have been implanted, the saddle points of thepedicles 314, 316, 318, 320 of the second, third, fourth, and fifthvertebrae 304, 306, 308, 310 may be reamed to provide semisphericalresections.

Referring to FIG. 11, a perspective view illustrates the portion of thespine 300 of FIG. 8 after reaming of the saddle points of the pedicles314, 316, 318, 320 to provide semispherical resections 354, 356, 358,360. More precisely, after the reaming operation has been carried out,the second vertebra 304 has semispherical resections 354, the thirdvertebra 306 has semispherical resections 356, the fourth vertebra 308has semispherical resections 358, and the fifth vertebra 310 hassemispherical resections 360. The semispherical resections 354 on thesecond vertebra 304 are optional, and may be omitted if desired.

Reaming may be accomplished through the use of a reamer (not shown) witha rotating, semispherical head having a longitudinal bore designed toreceive the protruding proximal ends of each of the guide wires 350.Thus, the guide wires 350 guide the reaming operations to ensure thatthe semispherical resections 354, 356, 358, 360 have the proper shapeand size. After reaming of the saddle points of the pedicles 314, 316,318, 320 has been carried out, the saddle points of the pedicles 314 ofthe second vertebra 304 may be further reamed and prepared to receivethe superior prostheses 34, 36 of the caudal facet joint assembly 24.Referring to FIG. 12, a perspective view illustrates the portion of thespine 300 of

FIG. 8 with a frame 370 registered on the third vertebra 306 tofacilitate formation of shaped resections on the saddle points of thepedicles 314 second vertebra 304. As shown, the frame 370 has a firstanchor 372, a second anchor 374, a first arm 376, a second arm 378, alocking mechanism 380, and an external anchoring feature 382.

The anchors 372, 374 have semispherical distal ends designed to fit intothe semispherical resections 356 of the third vertebra 306 in such amanner that the frame 370 can be oriented within the sagittal plane (notshown) to position it substantially perpendicular to the spine 300. Thefirst anchor 372 attached to the distal end of the first arm 376, andthe second anchor 374 is attached to the distal end of the second arm378.

The frame 370 permits relative translation between the first and secondarms 376, 378 along three perpendicular axes. Relative motion of thearms 376, 368 along all three axes may be locked through the use of alocking mechanism 380. The external anchoring feature 382 may be used tosecure the frame 370 to a stationary object such as an operating table.An articulating, lockable arm (not shown) or the like may be used togrip the substantially semispherical external anchoring feature 382 tokeep the frame 370 at its desired position and orientation.

In operation, the surgeon may position the anchors 372, 374 at thesemispherical resections 356 and then rotate the frame 370 to thedesired orientation while moving the arms 376, 378 as needed relative toeach other to keep the anchors 372, 374 on the semispherical resections356. Once the frame 370 is in the proper orientation (i.e., generallyperpendicular to the spine 300 and within the sagittal plane), thesurgeon may actuate the locking mechanism 380 to lock the positions ofthe arms 376, 378 relative to each other and secure the externalanchoring feature to the stationary object to keep the frame 370 in thedesired orientation.

As shown in FIG. 12, the first arm 376 has a first registration featuredesigned to receive one or more tools such as resection tools. Asembodied in FIG. 12, the first registration feature takes the form of afirst receiver 384 with a substantially rectangular bore. Similarly, thesecond arm 378 has a second receiver 386 with a substantiallyrectangular bore. The substantially rectangular bores of the receivers384, 386 are designed to receive corresponding protruding anchoringfeatures of the tools, and to retain the anchoring features in responseto actuation of clips 388 on the receivers 384, 386. The clips 388 maycompress the substantially rectangular bores to cause the receivers 384,386 to securely retain the protruding anchoring features of the tools.

A reamer with hollow reaming head (not shown) may be secured to each ofthe receivers 384, 386 and used to further ream the saddle points of thepedicles 314 of the second vertebra 304. The hollow reaming head mayengage the protruding proximal ends of the guide wires 350 attached tothe second vertebra 304, and may have a generally conical reamingsurface that forms shaped resections 394 in the second vertebra 304, asshown.

The shaped resections 394 may also have smaller holes for receiving thefingers of the bone apposition surfaces 90 of the superior prostheses34, 36 of the caudal facet joint assembly 24. The smaller holes may beformed through the use of a smaller reamer (not shown) applied throughthe openings of a template (not shown), or the like. After the shapedresections 394 have been formed on the second vertebra 304, the caudalfusion assembly 28 and the superior prostheses 34, 36 of the caudalfacet joint assembly 24 may be secured to the first and second vertebrae302, 304.

Referring to FIG. 13, a perspective view illustrates the portion of thespine 300 of FIG. 8 after attachment of the caudal fusion assembly 28and the superior prostheses 34, 36 of the caudal facet joint assembly 24of the system of FIG. 1 to the first and second vertebrae 302, 304. Moreprecisely, the guide wires 350 are removed and the pedicle screws 54 areimplanted in the pedicles 314 of the second vertebra 304, along thebores that remain after removal of the guide wires 350. The superiorprostheses 34, 36 are positioned on the second vertebra 304 such thatthe fingers of the bone apposition surfaces 90 engage the small holes ofthe shaped resections 394.

The pedicle screws 66 are implanted in the first vertebra 302. If thefirst vertebra 302 is S1, implantation of the pedicle screws 66 is notin a pedicle, but is carried out in a portion of the sacrum withsufficient bone mass to provide anchorage. This may be accomplishedthrough the use of any of a number of methods known in the art. Thepedicle screws 66 are implanted with the yoke assemblies 68 in place onthe proximal ends 158 of the pedicle screws 66.

The superior prostheses 60, 62 of the caudal fusion assembly 28 are thenpositioned such that the semispherical engagement surfaces 150 of thesuperior prostheses 60, 62 rest within the semispherical receivingsurfaces 92 of the superior prostheses 34, 36. The yoke assemblies 68,154 are then polyaxially rotatable relative to the first and secondvertebrae 302, 304, respectively. The yoke assemblies 68, 154 arerotated to the optimal orientations for receiving the rods 64, and therods 64 are positioned in the troughs 166 of the yoke assemblies 68,154. The nuts 168 are threaded into engagement with their associatedarms 162, 164 and tightened to keep the rod 64 in place and restrainfurther pivoting of the yoke assemblies 68, 154.

Then, the interpositional members 140, the split spheres 142, and therotational locking members 144 are inserted on the distal ends 132 ofeach of the pedicle screws 54 and tightened to restrict rotation of thesuperior prostheses 60, 62 relative to the pedicle screws 54. Thetranslational locking members 146 are then inserted on the distal ends132 of the pedicle screws 54 and tightened to restrict sliding of thesuperior prostheses 34, 36, 60, 62 away from the second vertebra 304.

This provides the configuration shown in FIG. 13, in which the caudalfusion assembly 28 and the superior prostheses 34, 36 of the caudalfacet joint assembly 24 are secured to the first and second vertebrae302, 304. Next, the pedicles 316 of the third vertebra 306 may befurther reamed like those of the second vertebra 304.

Referring to FIG. 14, a perspective view illustrates the portion of thespine 300 of FIG. 8 with the frame 370 registered on the fourth vertebra308 to facilitate formation of shaped resections 396 on the saddlepoints of the third vertebra 306. As shown, the frame 370 is seated onthe fourth vertebra 308 such that the anchors 372, 374 rest on thesemispherical resections 358. The frame 370 is used in substantially thesame manner set forth in the description of FIG. 12, except that theshaped resections 396 are formed on the saddle points of the thirdvertebra 306 instead of those of the second vertebra 304.

Thus, the third vertebra 306 is prepared to receive the superiorprostheses 44, 46. After the shaped resections 396 have been formed, thesuperior prostheses 44, 46 of the cephalad facet joint assembly 26 andthe inferior prostheses 38, 40 of the caudal facet joint assembly 24 maybe secured to the third vertebra 306.

Referring to FIG. 15, a perspective view illustrates the portion of thespine 300 of FIG. 8 after further attachment of the inferior prostheses38, 40 of the caudal facet joint assembly 24, the crosslink assembly 42,and the superior prostheses 44, 46 of the cephalad facet joint assembly26 of the system 10 of FIG. 1 to the portion of the spine 300. Moreprecisely, the guide wires 350 are removed and the pedicle screws 54 areimplanted in the pedicles 316 of the third vertebra 306, along the boresthat remain after removal of the guide wires 350. The superiorprostheses 44, 46 are positioned on the third vertebra 306 such that thefingers of the bone apposition surfaces 90 engage the small holes of theshaped resections 396.

The inferior prostheses 38, 40 of the caudal facet joint assembly 24 arethen positioned such that the semispherical engagement surfaces 100 ofthe inferior prostheses 38, 40 rest within the semispherical receivingsurfaces 92 of the superior prostheses 44, 46. The inferior prostheses38, 40 remain polyaxially rotatable relative to the superior prostheses44, 46.

The crosslink assembly 42 may then be loosely coupled to the inferiorprostheses 38, 40. If desired, the crosslink assembly 42 may be looselyassembled before it is coupled to the inferior prostheses 38, 40. Moreprecisely, the bolts 112 may be inserted through the implant couplingcomponents 110 and the rod coupling components 114, and the nuts 116 maybe loosely threaded onto the bolts 112. The ends of the rod 118 may beinserted into the rod coupling components. Then, the loosely assembledcrosslink assembly 42 may be positioned and the implant couplingcomponents 110 may be coupled to the inferior prostheses 38, 40.

The crosslink assembly 42 has not yet been tightened, and is thereforerelatively freely configurable. Thus, the inferior prostheses 38, 40 maybe rotated, with the crosslink assembly 42 coupled thereto, such thattheir articulation surfaces 104 are positioned to articulate optimallywith the articulation surfaces 94 of the superior prostheses 34, 36 ofthe caudal facet joint assembly 24. Once the articulation surfaces 104have reached the proper positions, the nuts 116 may be tightened on thebolts 112 to lock the configuration of the crosslink assembly 42,thereby providing a rigid bridge between the inferior prostheses 38, 40.

Then, the locking assemblies 56 may be used to restrict further rotationor translation of the inferior prostheses 38, 40 and the superiorprostheses 44, 46, as described previously, in connection with FIG. 13.Thus, the prostheses 38, 40, 44, 46 and the crosslink assembly 42 arerigidly and securely attached to the third vertebra 306. The saddlepoints of the fourth vertebra 308 may then be further resected toprepare the fourth vertebra 308 to receive the inferior prostheses 72,74 and the inferior prostheses 48, 50 of the cephalad facet jointassembly 26.

Referring to FIG. 16, a perspective view illustrates the portion of thespine 300 of FIG. 8 with the frame 370 registered on the fifth vertebra310 to facilitate formation of shaped resections 398 on the saddlepoints of the fourth vertebra 308. As shown, the frame 370 is seated onthe fifth vertebra 310 such that the anchors 372, 374 rest on thesemispherical resections 360. The frame 370 is used in substantially thesame manner set forth in the description of FIG. 12, except that theshaped resections 398 are formed on the saddle points of the fourthvertebra 308 instead of those of the second vertebra 304.

Thus, the fourth vertebra 308 is prepared to receive the inferiorprostheses 72, 74. After the shaped resections 398 have been formed, theinferior prostheses 72, 74 and the inferior prostheses 48, 50 of thecephalad facet joint assembly 26 may be secured to the fourth vertebra308.

Referring to FIG. 17, a perspective view illustrates the portion of thespine 300 of FIG. 8 after further attachment of the inferior prostheses72, 74 and the inferior prostheses 48, 50 of the cephalad facet jointassembly 26 to the portion of the spine 300. As shown, a complete system410 has been attached to the vertebrae 302, 304, 306, 308, 310. Thesystem 410 is similar to the system 10 of FIG. 1, except that the system410 fuses only one, and not two, levels cephalad to the cephalad facetjoint assembly 26. Accordingly, in place of the cephalad fusion assembly30 of FIG. 1, the system 410 has a cephalad fusion assembly 430 thatprovides fusion for just one motion segment. Thus, cephalad fusionassembly 430 has rods 476 that may be somewhat shorter than the rods 76of the cephalad fusion assembly 30 of FIG. 1.

In order to implant the remainder of the system 410, the guide wires 350are first removed from the pedicles 318 of the fourth vertebra 308 andthe pedicle screws 54 are implanted in the pedicles 318 of the fourthvertebra 308, along the bores that remain after removal of the guidewires 350. The inferior prostheses 72, 74 are positioned on the fourthvertebra 308 such that the fingers of the bone apposition surfaces 180engage the small holes of the shaped resections 398.

The inferior prostheses 48, 50 of the cephalad facet joint assembly 26are then positioned such that the semispherical engagement surfaces 100of the inferior prostheses 48, 50 rest within the semisphericalreceiving surfaces 182 of the inferior prostheses 72, 74. The inferiorprostheses 48, 50 remain polyaxially rotatable relative to the inferiorprostheses 72, 74.

The crosslink assembly 52 may then be loosely coupled to the inferiorprostheses 48, 50. If desired, the crosslink assembly 52 may be looselyassembled before it is coupled to the inferior prostheses 48, 50. Moreprecisely, the procedure set forth in the description of FIG. 15, forassembly of the crosslink assembly 42, may also be used for thecrosslink assembly 52.

The inferior prostheses 48, 50 may be rotated, with the crosslinkassembly 52 coupled thereto, such that their articulation surfaces 104are positioned to articulate optimally with the articulation surfaces 94of the superior prostheses 44, 46 of the cephalad facet joint assembly26. Once the articulation surfaces 104 have reached the properpositions, the crosslink 52 may be tightened to provide a rigid bridgebetween the inferior prostheses 48, 50.

Then, the locking assemblies 56 may be used to restrict further rotationor translation of the inferior prostheses 48, 50 and the inferiorprostheses 72, 74, as described previously, in connection with FIG. 13.Thus, the prostheses 48, 50, 72, 74 and the crosslink assembly 52 arerigidly and securely attached to the fourth vertebra 308.

The pedicle screws 66 are implanted in the pedicles 320 of the fifthvertebra 310. This may be accomplished by removing the guide wires 350and inserting the distal ends 160 of the pedicle screws 66 into thepedicles 320 through the bores left by removal of the guide wires 350.The pedicle screws 66 are implanted with the yoke assemblies 68 in placeon the proximal ends 158 of the pedicle screws 66.

The polyaxial rod connectors 78 may be installed in the semisphericalbores of the polyaxial receivers 184 of the inferior prostheses 72, 74by the manufacturer of the system 410, or by the surgeon. Thus, if thepolyaxial rod connectors 78 are not already in the semispherical boresof the polyaxial receivers 184, they may now be inserted therein. Thecaudal ends of the rods 476 may be inserted into the bores of thepolyaxial rod connectors 78. The polyaxial rod connectors 78 swivelwithin the polyaxial receivers 184 such that the cephalad ends of therods 476 can be placed in the troughs 166 of the yoke assemblies 68.

The yoke assemblies 68 are also polyaxially rotatable relative to thepedicle screws 66, and may thus be reoriented to receive the cephaladends of the rods 476 at the optimal angles. Once the cephalad ends havebeen placed in the troughs 166 of the optimally-oriented yoke assemblies68, the nuts 168 may be rotated into engagement with the walls 162, 164of the yoke assemblies 68 and tightened to secure the cephalad ends ofthe rods 476 to the yoke assemblies 68, and to restrict further rotationof the yoke assemblies 68 relative to the pedicle screws. The receiverfasteners 186 may also be tightened to restrict further rotation of thepolyaxial rod connectors 78 and the caudal ends of the rods 476 relativeto the inferior prostheses 72, 74.

Facet joint replacement for the joints between the second and thirdvertebrae 304, 306 and between the third and fourth vertebrae 306, 308is now complete. Additionally, fusion of the joint between the fourthand fifth vertebrae 308, 310 and fusion of the joint between the firstand second vertebrae 302, 304 have also been completed. Thus,implantation of the system 410 is complete, and the surgical wound sitemay be closed.

Referring to FIG. 18, a perspective view illustrates the portion of thespine 300 of FIG. 8 with the system 210 of FIG. 5 attached theretoinstead of the system 410 of FIG. 17. As in FIG. 5, the fusionassemblies 28, 30 have been omitted, and the engagement members 242 andin-growth cups 272 of FIGS. 6 and 7, respectively, have been included tocompensate for the omission.

Accordingly, the caudal and cephalad facet joint assemblies 24, 26 havebeen secured to the second, third, and fourth vertebrae 304, 306, 308 toprovide facet joint replacement for the joints between the second andthird vertebrae 304, 306 and between the third and fourth vertebrae 306,308. No fusion has been carried out. Thus, natural articulation maycontinue in the joint between the fourth and fifth vertebrae 308, 310and in the joint between the first and second vertebrae 302, 304. Thoseof skill in the art will appreciate that the systems 10, 210, 410 aremerely exemplary, and that many different systems may be envisioned withthe aid of the present disclosure, incorporating facet joint replacementof one or more motion segments with or without fusion.

In addition to the surgical flexibility provided by the presentinvention, the present invention also opens new possibilities forrevision. For example, the system 210 of FIG. 18 may be revised toprovide caudal and/or cephalad adjacent-level fusion by removing theengagement members 242 and/or the in-growth cups 272, and replacing themwith the caudal fusion assembly 28 and the split spheres 142 and/or withone of the cephalad fusion assemblies 30, 430.

Furthermore, facet joint replacement hardware such as the facet jointassemblies 24, 26 may be used to replace existing fusion assemblies suchas the fusion assemblies 28, 30, or fusion assemblies currently in usein orthopedics. Similarly, facet joint replacement assemblies 24, 26 maybe replaced with fusion hardware such as the fusion assemblies 28, 30.Additional levels of fusion or facet joint replacement may be added to asystem of any configuration according to the invention. Advantageously,the pedicle screws 54 and 66 do not require bone cement, and may thus berelatively freely removable from the vertebrae 302, 304, 306, 308, 310in the event that a reversal of a facet joint replacement or fusionprocedure is desired.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. It isappreciated that various features of the systems and methods describedabove can be mixed and matched to form a variety of other alternatives.As such the described embodiments are to be considered in all respectsonly as illustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. An implantable system comprising: a fusionassembly comprising a first yoke assembly and a first pedicle screw,wherein the yoke assembly is capable of polyaxial movement relative tothe first pedicle screw, wherein the pedicle screw includes a headportion and a shaft portion extending therefrom for inserting into abone member, the fusion assembly further comprising a rod that extendsthrough the yoke assembly and a second yoke assembly operably connectedto the rod, and a prosthetic assembly comprising a second pedicle screw,wherein the prosthetic assembly is capable of articular movement,wherein the second pedicle screw comprises a second shaft portion, andwherein at least a portion of the fusion assembly is nested in theprosthetic assembly such that the second yoke assembly of the fusionassembly shares the second pedicle screw with the prosthetic assembly,wherein the prosthetic assembly comprises a first annular member thatextends around the second shaft portion, wherein the fusion assemblycomprises a second annular member that extends around the second shaftportion.
 2. The system of claim 1, wherein the fusion assembly comprisesa semispherical engagement surface.
 3. The system of claim 2, whereinthe semispherical engagement surface of the fusion assembly is nested ina receiving surface of the prosthetic assembly.
 4. The system of claim3, further comprising a locking assembly received on the second pediclescrew above the semispherical engagement surface and the receivingsurface.
 5. The system of claim 4, wherein the locking assemblycomprises a rotational locking member and a translational lockingmember.
 6. The system of claim 1, wherein a receiving surface of theprosthetic assembly is attached to a first articulation surfaceconfigured to articulate with a second articulation surface of anadjacent prosthetic assembly.
 7. The system of claim 1, wherein theprosthetic assembly comprises a facet joint assembly.
 8. The system ofclaim 1, wherein the fusion assembly further comprises a nut designed totighten the rod therein.
 9. The system of claim 1, wherein a receivingsurface of the prosthetic assembly comprises a concave, semisphericalshape.
 10. An implantable system comprising: a fusion assemblycomprising a first yoke assembly and a second yoke assembly connectedvia a rod, wherein the second yoke assembly includes an engagementsurface attached thereto, and a prosthetic assembly, wherein theprosthetic assembly is capable of articular movement, wherein theengagement surface of the fusion assembly is nested within a receivingsurface of the prosthetic assembly such that the second yoke assembly ofthe fusion assembly shares a pedicle screw with the prosthetic assembly,wherein the pedicle screw comprises a shaft, wherein the prostheticassembly comprises a first annular member that extends around the shaftand the fusion assembly comprises a second annular member that extendsaround the shaft.
 11. The system of claim 10, wherein the fusionassembly is configured to extend across a first vertebral level and theprosthetic assembly is configured to extend across a second vertebrallevel.
 12. The system of claim 10, wherein the prosthetic assemblyfurther comprises an articulation surface attached to the receivingsurface.
 13. The system of claim 12, wherein the prosthetic assemblyfurther comprises a bone apposition surface.
 14. The system of claim 10,wherein the prosthetic assembly further comprises a locking member. 15.An implantable system comprising: a first fusion assembly comprising afirst yoke assembly and a first pedicle screw, wherein the first fusionassembly is configured to extend across a first vertebral level, aprosthetic assembly capable of articular movement, wherein theprosthetic assembly is configured to extend across a second vertebrallevel, wherein a portion of the prosthetic assembly and a portion of thefirst fusion assembly are connected at a single pedicle screw, whereinthe single pedicle screw comprises a shaft, wherein the portion of theprosthetic assembly connected at the single pedicle screw comprises afirst annular member that extends around the shaft, wherein the portionof the first fusion assembly connected at the single pedicle screwcomprises a second annular member that extends around the shaft, and asecond fusion assembly comprising a second yoke assembly a secondpedicle screw, wherein the second fusion assembly is configured toextend across a third vertebral level, wherein at least a portion of thefirst fusion assembly nests within the prosthetic assembly.
 16. Thesystem of claim 15, wherein the first fusion assembly and the secondfusion assembly provide fixation, while the prosthetic assembly providesmovement.
 17. The system of claim 15, wherein the prosthetic assemblycomprises a facet joint assembly.